Providing cqi feedback to a transmitter station in a closed-loop mimo system

ABSTRACT

Methods and apparatuses for reducing an amount of bandwidth required for feedback to a transmitter station in a closed-loop multiple-input multiple-output (MIMO) system are described herein. The methods may include initially measuring at a receiver station channel qualities associated with receiving signals from a transmitter station for a first and a second spatial channel, the transmitter and receiver stations employing a closed-loop MIMO system. The receiver station may then determine a first and a second channel quality indicator (CQI) based on the measured channel qualities and may then transmit to the transmitter station the first and the second CQI to directly and indirectly identify a first and a second modulation coding scheme (MCS) entry among a plurality of ordered MCS entries, respectively. The second MCS entry being one of a selected subset of lower ordered MCS entries relative to the first MCS entry. The transmitter station may selectively use the first and the second identified MCS to transmit signals to the receiver station over the first and the second spatial channel, respectively.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 60/796,768 filed May 1, 2006 entitled “METHODS ANDAPPARATUS FOR PROVIDING A CHANNEL QUALITY INDICATOR FEEDBACK SYSTEM FORBEAMFORMED CHANNELS ASSOCIATED WITH A MULTIPLE-INPUT-MULTIPLE-OUTPUTSYSTEM.” The present application claims priority to the 60/796,768provisional patent application.

TECHNICAL FIELD

Embodiments of the present invention relate to the field of wirelesscommunication systems, more specifically, to methods and apparatuses forproviding channel quality indicator (CQI) feedback for closed loopmultiple-input multiple-output (MIMO) systems.

BACKGROUND

As wireless communication becomes more and more popular at offices,homes, schools, etc., different wireless technologies and applicationsmay work in tandem to meet the demand for computing and communicationsat anytime and/or anywhere. For example, a variety of wirelesscommunication networks may coexist to provide a wireless environmentwith more computing and/or communication capability, greater mobility,and/or eventually seamless roaming.

In particular, wireless personal area networks (WPANs) may offer fast,short-distance connectivity within a relatively small space such as anoffice workspace or a room within a home. Wireless local area networks(WLANs) may provide broader range than WPANs within office buildings,homes, schools, etc. Wireless metropolitan area networks (WMANs) maycover a greater distance than WLANs by connecting, for example,buildings to one another over a broader geographic area. Wireless widearea networks (WWANs) may provide the broadest range as such networksare widely deployed in cellular infrastructure. Although each of theabove-mentioned wireless communication networks may support differentusages, coexistence among these networks may provide a more robustenvironment with anytime and anywhere connectivity.

Some wireless networks, such as WMAN, may employ a communicationtechnique known as multiple-input multiple-output (MIMO). In MIMO, anetwork node such as a base station or a subscriber station maycommunicate with another node using multiple antennas. The multipleantennas may be used to communicate with the other node using multiplespatial channels. There are at least two types of MIMO systems, an openloop MIMO system and a closed loop MIMO system. In an open loop system,the transmitting node may transmit data signals to the receiving nodewithout first receiving feedback information from the receiving node tofacilitate such communication. In contrast, in a closed loop system, thetransmitting node may receive from the receiving node feedbackinformation prior to transmitting data signals to the receiving node.Such feedback information may better facilitate the transmission of thedata signals to the receiving node.

The feedback information provided back to the transmitting node mayinclude channel quality indicators (CQIs). Typically, one CQI isprovided for one spatial channel. In some cases, a CQI may specify amodulation coding scheme (MCS) that may indicate a modulation level anda code rate for the transmitting node to use in order to facilitate thetransmitting node to efficiently transmit signals to the receiving node.Note that in other instances, a CQI may specify other types of channelquality indicator such as a signal-to-interference plus noise ratio(SINR), a signal-to-noise ratio (SNR), and so forth, of the spatialchannel associated with the CQI. Unfortunately, feedback such as CQIsmay consume large amounts of the feedback bandwidth, thus reducing theoverall performance of the wireless network.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be readily understood by thefollowing detailed description in conjunction with the accompanyingdrawings. To facilitate this description, like reference numeralsdesignate like structural elements. Embodiments of the invention areillustrated by way of example and not by way of limitation in thefigures of the accompanying drawings.

FIG. 1 illustrates an example wireless communication system inaccordance with various embodiments of the present invention;

FIG. 2 illustrates an example multiple-input multiple-output (MIMO)system in accordance with various embodiments of the present invention;

FIG. 3 illustrates an example subscriber station in accordance withvarious embodiments of the present invention;

FIG. 4 illustrates channel quality indicators (CQIs) specifyingmodulation coding scheme (MCS) entries in a table having ordered MCSentries according to conventional techniques;

FIG. 5 illustrates CQIs specifying MCS entries in a table having orderedMCS entries in accordance with various embodiments of the presentinvention;

FIG. 6A illustrates an MCS probability density distribution and aselected subset of non-continuous lower ordered MCS entries inaccordance with various embodiments of the present invention;

FIG. 6B illustrates the MCS probability density distribution and theselected subset of non-continuous lower ordered MCS entries of FIG. 6Asuperimposed on top of the tables of FIGS. 4 and 5 in accordance withvarious embodiments of the present invention;

FIG. 7 illustrates a process in accordance with various embodiments ofthe present invention;

FIG. 8 illustrates an apparatus in accordance with various embodimentsof the present invention; and

FIG. 9 illustrates an example system in accordance with variousembodiments of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof wherein like numeralsdesignate like parts throughout, and in which is shown by way ofillustration embodiments in which the invention may be practiced. It isto be understood that other embodiments may be utilized and structuralor logical changes may be made without departing from the scope of thepresent invention. Therefore, the following detailed description is notto be taken in a limiting sense, and the scope of embodiments inaccordance with the present invention is defined by the appended claimsand their equivalents.

Various operations may be described as multiple discrete operations inturn, in a manner that may be helpful in understanding embodiments ofthe present invention; however, the order of description should not beconstrued to imply that these operations are order dependent.

For the purposes of the instant description, the phrase “A/B” means A orB. For the purposes of the instant description, the phrase “A and/or B”means “(A), (B), or (A and B).” For the purposes of the instantdescription, the phrase “at least one of A, B and C” means “(A), (B),(C), (A and B), (A and C), (B and C) or (A, B and C).” For the purposesof the instant description, the phrase “(A)B” means “(B) or (AB),” thatis, A is an optional element.

The description may use the phrases “in various embodiments,” or “insome embodiments,” which may each refer to one or more of the same ordifferent embodiments. Furthermore, the terms “comprising,” “including,”“having,” and the like, as used with respect to embodiments of thepresent invention, are synonymous.

According to various embodiment of the invention, methods andapparatuses are provided that may reduce the amount of bandwidthrequired to provide channel quality feedback to a transmitter stationfrom a receiver station, to enable the transmitter station to adapt andconfigure sending of data signals to the receiver station. For theembodiments, the receiver and transmitter stations may employ aclosed-loop MIMO system. The methods may include initially measuring ata receiver station channel qualities associated with receiving signalsfrom a transmitter station for a first and a second spatial channel. Thereceiver station may then transmit to the transmitter station at least afirst and a second channel quality indicator (CQI) to directly andindirectly identify a first and a second modulation coding scheme (MCS)entry among a plurality of ordered MCS entries, respectively, the firstand second MCS entries correspondingly identifying a first and a secondMCS, and the CQIs having been determined based at least in part on themeasured channel qualities. In some instances, the second MCS entry maybe one of a selected subset of non-continuous or continuous lowerordered MCS entries relative to the first MCS entry, the first and thesecond MCS to be used by the transmitter station to transmit signals tothe receiver station over the first and the second spatial channel,respectively. Not that the phrase “lower ordered” as used herein may beanalogous to, for example, lower level or lower quality. These and otheraspects of various embodiments of the present invention will bedescribed in greater detail below.

Referring to FIG. 1, an example wireless communication system 100 mayinclude one or more wireless communication networks, generally shown as110, 120, and 130. In particular, the wireless communication system 100may include a wireless personal area network (WPAN) 110, a wirelesslocal area network (WLAN) 120, and a wireless metropolitan area network(WMAN) 130. Although FIG. 1 depicts three wireless communicationnetworks, the wireless communication system 100 may include additionalor fewer wireless communication networks. For example, the wirelesscommunication system 100 may include additional WPANs, WLANs, and/orWMANs. The methods and apparatus described herein are not limited inthis regard.

The wireless communication system 100 may also include one or moresubscriber stations, generally shown as 140, 142, 144, 146, and 148. Forexample, the subscriber stations 140, 142, 144, 146, and 148 may includewireless electronic devices such as a desktop computer, a laptopcomputer, a handheld computer, a tablet computer, a cellular telephone,a pager, an audio and/or video player (e.g., an MP3 player or a DVDplayer), a gaming device, a video camera, a digital camera, a navigationdevice (e.g., a GPS device), a wireless peripheral (e.g., a printer, ascanner, a headset, a keyboard, a mouse, etc.), a medical device (e.g.,a heart rate monitor, a blood pressure monitor, etc.), and/or othersuitable fixed, portable, or mobile electronic devices. Although FIG. 1depicts five subscriber stations, the wireless communication system 100may include more or less subscriber stations.

The subscriber stations 140, 142, 144, 146, and 148 may use a variety ofmodulation techniques such as spread spectrum modulation (e.g., directsequence code division multiple access (DS-CDMA) and/or frequencyhopping code division multiple access (FH-CDMA)), time-divisionmultiplexing (TDM) modulation, frequency-division multiplexing (FDM)modulation, orthogonal frequency-division multiplexing (OFDM)modulation, multi-carrier modulation (MDM), and/or other suitablemodulation techniques to communicate via wireless links. In one example,the laptop computer 140 may operate in accordance with suitable wirelesscommunication protocols that require very low power such as Bluetooth®,ultra-wide band (UWB), and/or radio frequency identification (RFID) toimplement the WPAN 110. In particular, the laptop computer 140 maycommunicate with devices associated with the WPAN 110 such as the videocamera 142 and/or the printer 144 via wireless links.

In another example, the laptop computer 140 may use direct sequencespread spectrum (DSSS) modulation and/or frequency hopping spreadspectrum (FHSS) modulation to implement the WLAN 120 (e.g., the 802.11family of standards developed by the Institute of Electrical andElectronic Engineers (IEEE) and/or variations and evolutions of thesestandards). For example, the laptop computer 140 may communicate withdevices associated with the WLAN 120 such as the printer 144, thehandheld computer 146 and/or the smart phone 148 via wireless links. Thelaptop computer 140 may also communicate with an access point (AP) 150via a wireless link. The AP 150 may be operatively coupled to a router152 as described in further detail below. Alternatively, the AP 150 andthe router 152 may be integrated into a single device (e.g., a wirelessrouter).

The laptop computer 140 may use OFDM modulation to transmit largeamounts of digital data by splitting a radio frequency signal intomultiple small sub-signals, which in turn, are transmittedsimultaneously at different frequencies. In particular, the laptopcomputer 140 may use OFDM modulation to implement the WMAN 130. Forexample, the laptop computer 140 may operate in accordance with the802.16 family of standards developed by IEEE to provide for fixed,portable, and/or mobile broadband wireless access (BWA) networks (e.g.,the IEEE std. 802.16-2004 (published Sep. 18, 2004), the IEEE std.802.16e (published Feb. 28, 2006), the IEEE std. 802.16f (published Dec.1, 2005), etc.) to communicate with base stations, generally shown as160, 162, and 164, via wireless link(s). Further, in some instances,communication within the WMAN between, for example, base stations andsubscriber stations, may be via MIMO, such as closed-loop MIMO.

Although some of the above examples are described above with respect tostandards developed by IEEE, the methods and apparatus disclosed hereinare readily applicable to many specifications and/or standards developedby other special interest groups and/or standard developmentorganizations (e.g., Wireless Fidelity (Wi-Fi) Alliance, WorldwideInteroperability for Microwave Access (WiMAX) Forum, Infrared DataAssociation (IrDA), Third Generation Partnership Project (3GPP), etc.).The methods and apparatus described herein are not limited in thisregard.

The WLAN 120 and WMAN 130 may be operatively coupled to a common publicor private network 170 such as the Internet, a telephone network (e.g.,public switched telephone network (PSTN)), a local area network (LAN), acable network, and/or another wireless network via connection to anEthernet, a digital subscriber line (DSL), a telephone line, a coaxialcable, and/or any wireless connection, etc. In one example, the WLAN 120may be operatively coupled to the common public or private network 170via the AP 150 and/or the router 152. In another example, the WMAN 130may be operatively coupled to the common public or private network 170via the base station(s) 160, 162, and/or 164.

The wireless communication system 100 may include other suitablewireless communication networks. For example, the wireless communicationsystem 100 may include a wireless wide area network (WWAN) (not shown).The laptop computer 140 may operate in accordance with other wirelesscommunication protocols to support a WWAN. In particular, these wirelesscommunication protocols may be based on analog, digital, and/ordual-mode communication system technologies such as Global System forMobile Communications (GSM) technology, Wideband Code Division MultipleAccess (WCDMA) technology, General Packet Radio Services (GPRS)technology, Enhanced Data GSM Environment (EDGE) technology, UniversalMobile Telecommunications System (UMTS) technology, Third GenerationPartnership Project (3GPP) technology, standards based on thesetechnologies, variations and evolutions of these standards, and/or othersuitable wireless communication standards. Although FIG. 1 depicts aWPAN, a WLAN, and a WMAN, the wireless communication system 100 mayinclude other combinations of WPANs, WLANs, WMANs, and/or WWANs. Themethods and apparatus described herein are not limited in this regard.

The wireless communication system 100 may include other WPAN, WLAN,WMAN, and/or WWAN devices (not shown) such as network interface devicesand peripherals (e.g., network interface cards (NICs)), access points(APs), redistribution points, end points, gateways, bridges, hubs, etc.to implement a cellular telephone system, a satellite system, a personalcommunication system (PCS), a two-way radio system, a one-way pagersystem, a two-way pager system, a personal computer (PC) system, apersonal data assistant (PDA) system, a personal computing accessory(PCA) system, and/or any other suitable communication system. Althoughcertain examples have been described above, the scope of coverage ofthis disclosure is not limited thereto.

Referring to FIG. 2, which illustrates an example wireless MIMO system200 that may include a base station 210 (having multiple antennas252-258) and one or more subscriber stations, generally shown as 220 and225 in accordance with various embodiments of the present invention. Thewireless MIMO system 200 may include a point-to-point MIMO system and/ora point-to-multiple point MIMO system. For example, a point-to-pointMIMO system may include the base station 210 and the subscriber station220. A point-to-multiple point MIMO system may include the base station210 and the subscriber station 225. The base station 210 may transmitdata streams to the subscriber stations 220, 225 simultaneously viamultiple spatial channels. For example, the base station 210 maytransmit two data streams (via two spatial channels) to the subscriberstation 220 and one data stream to the subscriber station 225 (via onespatial channel). Each spatial channel linking the subscriber stations220 and 225 to the base station 210 may each be associated with anantenna of the receiving stations (e.g., subscriber stations 220 and225). Thus, in this case, subscriber station 220 is linked to basestation 210 via two spatial channels while subscriber station 225 islinked to base station 210 via one spatial channel. Although FIG. 2 maydepict two subscriber stations 220 and 225, the wireless MIMO system 200may include additional subscriber stations in alternative embodiments.Further, although subscriber station 220 is depicted as having twoantennas and subscriber station 225 is depicted as having one antenna,in alternative embodiments, the subscriber stations 220 and 225 may haveother number of antennas. Similarly, in alternative embodiments, thebase station 210 may have other number of antennas rather than the fourantennas depicted in FIG. 2.

If the MIMO system 200 is a closed-loop MIMO system then prior to, forexample, the base station 210 (i.e., transmitter station) transmittingdata signals to subscriber station 220 (i.e., receiver station), thesubscriber station 220 may measure previously received signals from thebase station 210 received via the spatial channels linking the two.Based on the received signals, the subscriber station 220 may determinethe channel qualities of the two spatial channels. As a result of thechannel quality determinations, the subscriber station 220 may transmitto the base station 210, feedback information containing at least twoCQIs for the two spatial channels. In some embodiments, the two CQIs mayinclude modulation coding schemes (MCSs) for the two spatial channels.Once the base station 210 receives the two CQIs from the subscriberstation 220, the base station 210 may set the modulation levels and thecode rates for the spatial channels to be used for transmitting datasignals to the subscriber station 220.

FIG. 3 illustrates a subscriber station in accordance with variousembodiments of the present invention. The subscriber station 300 mayinclude a channel response predictor 310, a feedback informationgenerator 320, a network interface device (NID) 340, a processor 350,and a memory 360. The channel response predictor 310, the feedbackinformation generator 320, the NID 340, the processor 350, and thememory 360 may be operatively coupled to each other via a bus 370. WhileFIG. 3 depicts components of the subscriber station 300 coupled to eachother via the bus 370, these components may be operatively coupled toeach other via other suitable direct or indirect connections (e.g., apoint-to-point connection or a point-to-multiple point connection).

The NID 340 may include a receiver 342, a transmitter 344, and anantenna 346. The subscriber station 300 may receive and/or transmit datavia the receiver 342 and the transmitter 344, respectively. The antenna346 may include one or more directional or omnidirectional antennas suchas dipole antennas, monopole antennas, patch antennas, loop antennas,microstrip antennas, and/or other types of antennas suitable fortransmission of radio frequency (RF) signals. Although FIG. 3 depicts asingle antenna, the subscriber station 220 may include additionalantennas. For example, the subscriber station 300 may include aplurality of antennas to implement a multiple-input multiple-output(MIMO) system.

Although the components shown in FIG. 3 are depicted as separate blockswithin the subscriber station 300, the functions performed by some ofthese blocks may be integrated within a single semiconductor circuit ormay be implemented using two or more separate integrated circuits. Forexample, although the receiver 342 and the transmitter 344 are depictedas separate blocks within the NID 340, the receiver 342 may beintegrated into the transmitter 344 (e.g., a transceiver). The methodsand apparatus described herein are not limited in this regard.

In general, channel quality indicator (CQI) feedback, as brieflyintroduced previously, is widely used in WMAN systems for scheduling andlink adaptation. It consumes most of the feedback bandwidth. Foropen-loop multiple-input multiple-output (MIMO) system, CQI for eachantenna (or spatial channel or layer) is fed back from a receiverstation (i.e., subscriber station) to a transmitter station (i.e., basestation) based on the measurements of previously received signalsreceived by the receiver station from the transmitter station via thespatial channels linking the two. Such measurements may allow thereceiver station to determine the channel qualities of the spatialchannels. In conventional MIMO systems, because the CQIs of the antennasof the MIMO link can be in any order, feedback provided back to thetransmitter station (i.e., base station) may consume more bits thanthose when the qualities are ordered. For closed-loop MIMO, whenbeamforming vectors for each of the spatial channels formed by theantennas are provided by a subscriber station and fed back to a basestation, they may be arranged in order according to channel qualities ofthe spatial channels that are associated with the beamforming vectors.Given the beamforming vectors are already fed back, the CQIs that arefed back to the base station and that correspond to the beamformingvectors (as well as their associated spatial channels) may also beordered. Leveraging on the order, the bits needed for the CQIs that arefed back to the base station, thus in turn, the overall bandwidthrequired, may be reduced in accordance with various embodiments of thepresent invention.

An example of CQI for per antenna rate control (PARC) system and openloop MIMO is illustrated in FIG. 4. In particular, FIG. 4 shows a tablecomprising a plurality of ordered MCS entries, each of the MCS entriesbeing associated with a different level of channel quality. As depicted,there are 32 entries in the table and each entry correspondinglyidentifying a different MCS. The channel quality decreases with theentry index. For example, entry thirty one, which is at the bottom ofthe table (i.e., MCS31), may be associated with the best quality channelamong a set of exemplary spatial channels associated with the MCSentries of the table while entry zero, at the top of the table (i.e.,MCS0), may be associated with the worst quality channel among a set ofexemplary spatial channels associated with the MCS entries of the table.Thus, in this table, MCS31 is a higher order entry than MCS0. Similarly,MCS9 is a higher order entry than MCS7. Resultantly, the table depictedin FIG. 4 shows a plurality of ordered MCS entries. Each of the MCSentries in the table may be associated with a modulation level and aforward error correction (FEC) code rate. Thus, although not depicted,the table essentially has two dimensions, one along the modulation leveland the other along the FEC code rate. The two dimensions collapse intoone sorted by channel quality. Thus, each combination of modulationlevel and FEC code rate may map to one channel quality. As a result, alower modulation level and/or a lower code rate may be employed for aspatial channel with lower quality.

As previously described, a subscriber station (e.g., the subscriberstation 220 of FIG. 2) may feed back a CQI for each of its spatialchannels to facilitate data signal transmission from the base station(e.g., base station 210). For example, suppose subscriber station 220has three antennas instead of the two as depicted in FIG. 2, thesubscriber station 220 may then send to the base station 210 three CQIs(i.e., CQI 1, CQI 2, and CQI 3) for three spatial channels (e.g.,spatial channels 1, 2, and 3) prior to the base station 210 sending datasignals to the subscriber station 220. Under conventional techniques,the three CQIs provided back to the base station 210 may be in randomorder. Thus, CQI 1, CQI 2, and CQI 3 that are transmitted back to thebase station 210 will, as depicted in FIG. 4, identify entries for MCS7,MCS5, and MCS9, respectively.

The CQIs may identify MCS entries either directly or indirectly by, forexample, indexing to a plurality of ordered MCS entries as shown in FIG.4. Some conventional systems may use 5, 3, and 3 bits to identify thethree MCS entries for the three CQIs. That is, both the base station 210and the subscriber station 220 may be provisioned with a table ofordered MCS entries such as depicted in FIG. 4 that, together with the5, 3, and 3 bit CQIs provided by the subscriber station 220, may allowthe base station 210 to be able to determine the MCS entries specifiedby the CQIs having 5, 3, and 3 bits. For example, in conventionalsystems, CQI 1 may include 5 bits (e.g., 2⁵=32 entries) to directlyidentify an MCS entry among 32 MCS entries, and CQI 2 (or 3) may include3 bits to indirectly identify another entry in an 8-entry neighborhoodof CQI 1's entry. Because of the random nature of conventional systems,under conventional systems, CQI 3 (as well as CQI 2) can identify an MCSentry that is a lower or a higher order MCS entry than the MCS entryidentified by CQI 1. In this case, CQI 3 identifies entry MCS9 which isa higher order entry than the entry (i.e., entry MCS 7) identified byCQI 1. Because of the greater dynamic range or variation of CQI 3 andCQI 2, with respect to CQI 1, more bits may be needed to specify them ascompared to, for example, if the CQI 3 and CQI 2 could only be smallerthan CQI.

In general, the methods and apparatuses described herein may reduce theamount of bandwidth required for channel feedback for beamformed MIMOsystems. The methods and apparatuses described herein are not limited inthis regard. For beamformed (or precoded ) MIMO, beamforming vectors fora set of spatial channels may be fed back to a transmitter station froma receiver station and the vectors may be ordered in accordance withchannel quality. This means that the quality of the spatial channel thatcorresponds to a first beamforming vector may be the best among a set ofspatial channels and the quality of the spatial channel that correspondsto a second beamforming vector may be the second best among the set ofspatial channels, wherein the set of spatial channels maycommunicatively link the receiver station to the transmitter station. Asa result, the CQIs associated with the set of spatial channels and theirassociated beamforming vectors may also be ordered. Note that a channelquality may be measured at the output of a MIMO decoder that may employzero-forcing, minimize mean square error (MMSE), successive interferencecancellation, parallel interference cancellation, and/or otherprocesses.

Because of the ordered beamforming vectors provided to the transmitterstation (i.e., base station 210), a determination can be made at thetransmitter station as to which CQI from the group of CQIs received fromthe receiver station (e.g., subscriber station 220) will be associatedwith the highest quality spatial channel among the set of spatialchannels communicatively linking the transmitter station to the receiverstation. The CQI determined to be associated with the highest qualitychannel may also specify, in a plurality of ordered MCS entries, thehighest ordered MCS entry relative to the other MCS entries to bedirectly or indirectly identified by the other CQIs. This is illustratedin FIG. 5 in which CQI 1 directly identifies the highest MCS entryrelative to the MCS entries that may be indirectly identified by CQI 2and CQI 3. Notice that the words “directly” and “indirectly” are usedhere. This is because, CQI 1 may need five bits to identify an MCS entry(thus “directly” identify) from the 32 entries while CQI 2 and CQI 3 mayneed fewer bits to identify their corresponding MCS entries (thus“indirectly” identify) since the MCS entries for CQI 2 and CQI 3 will belower order MCS entries relative to the MCS identified by CQI 1. Thatis, the MCS entries for CQI 2 and CQI 3 will be, in the ordered MCSentries table, lower ordered MCS entries relative to the MCS entryidentified by CQI 1. Thus, the MCS entries for CQI 2 and 3 will not haveto be fully identified (i.e., 5 bit identification) because the MCSentries for CQI 2 and 3 can be identified by referencing or indexingthem relative to the MCS entry identified by CQI 1 as will be describedin greater detail below. As a result, CQI 2 and CQI 3 may need fewerbits for identification of their respective MCS entries so long as theidentity of the MCS entry for CQI 1 is known. Thus, according to variousembodiments of the present invention, this order of the CQIs may beexploited in order to reduce the amount of bandwidth required for CQIfeedback for the beamformed spatial channels.

The reduction in bandwidth required for CQI feedback may be furtherfacilitated by generically or non-generically determining a probabilitydensity distribution (i.e., probability density function) for a secondspatial channel given a first spatial channel as illustrated in FIG. 6A.Such a statistical distribution may also be an MCS probability densitydistribution for a second MCS entry given a first MCS entry. Bygenerating such a statistical distribution, the bits needed in order toidentify a second MCS entry (as indirectly identified by a second CQI,i.e., CQI 2) given a first MCS entry (as directly identified by a firstCQI, i.e., CQI 1) may be reduced. Such a statistical distribution may begenerated by, for example, randomly generating many beamformed channelsand computing a first and a second CQI (CQI 1 and CQI 2) both using 5bits, and collecting the statistics about the difference between CQI 1and 2, i.e., CQI 1-CQI 2. The empirical probability density distributionof the difference can then be computed. The MCS probability densitydistribution may then be used to pre-determine a selected subset ofnon-continuous lower ordered MCS entries depicted as S2 in FIG. 6A. Notethat the terms probability density distribution and probability densityfunction will be used, herein, interchangeably, and are therefore,synonymous.

Members of the selected subset of non-continuous lower ordered MCSentries (herein “selected subset”) are candidate MCS entries, one ofwhich may be indirectly identified by CQI 2. Given the size of S2, e.g.,4, the pattern of S2 can be computed. In this illustration, the firstMCS entry is MCS i (as identified by CQI 1). Given the first MCS, MCS i,the four members of the selected subset based on the statisticaldistribution are entries MCS i-2, MCS i-3, MCSi-5, and MCS i-8, whichare successively lower ordered MCS entries. In some embodiments, theselected subset of MCS entries, MCS i-2, MCS i-3, MCSi-5, and MCS i-8,may be generic, thus may be used regardless of the value of the firstMCS (i.e., the value of “i” in MCS i). Alternatively, the selectedsubset of MCS entries may not be generic and may be dependent upon thevalue of the first MCS. Although the selected subset of MCS entries, MCSi-2, MCS i-3, MCSi-5, and MCS i-8, are successively lower ordered MCSentries, some successive members of the selected subset may not beimmediately successive.

For example, a non-member of the subset, entry MCS i-4, is betweensubset members MCS i-3 and MCS i-5. Similarly, non-members of thesubset, entries MCS i-6 and MCS i-7, are between subset members MCS i-5and MCS i-8. This is as a result of the MCS probability densitydistribution and the lower probability density as you move away from thegiven first MCS entry (i.e., MCS i). As a result, the selected subset isnon-continuous. However, in alternative embodiments, the selected subsetmay be continuous (i.e., no non-members disposed between the members ofthe selected subset).

Further, the MCS entries of the selected subset are lower ordered MCSentries because members of the subset are of lower order than the firstMCS entry (i.e., MCS i). In this example, CQI 1 may directly index thefirst MCS entry (MCS i) in a plurality of ordered MCS entries (i.e., thetable of FIG. 6A), while CQI 2 may indirectly index a second MCS entrythat is from within the selected subset of non-continuous lower orderedMCS entries relative to the indexed first MCS entry.

Note that the MCS probability density distribution and/or the selectedsubset, as previously alluded to, may be generic, thus the MCSprobability density distribution and/or the selected subset may be usedto determine a third MCS entry for a third CQI (CQI 3) given the secondMCS entry (as indirectly identified by CQI 2). Of course, once the thirdMCS entry is determined for the third CQI, the third CQI, which mayindirectly identify the third MCS entry, may be transmitted to thetransmitter station. This process for indirectly identifying MCS entriesfor CQIs other than CQI 1 (associated with the highest quality channel)may be repeated over and over again for additional CQIs if additionalCQIs for additional spatial channels are to be transmitted to thetransmitter station using the same generic MCS probability densitydistribution and/or the selected subset. Alternatively, the MCSprobability density distribution and/or the selected subset may not begeneric and may be dependent upon, for example, the value of first CQI(e.g., first MCS identified by the first CQI). In such cases, the MCSprobability density distribution and/or the selected subset may need tobe determined for each additional CQI.

In some embodiments, the MCS probability density distribution and/or theresulting selected subset may be generated by the receiver station(e.g., subscriber station 220) and the transmitter station (e.g., basestation 210) may be provisioned with the MCS probability densitydistribution and/or the selected subset to facilitate the transmitterstation to determine the MCS entries that may be indirectly identifiedby CQIs provided by the receiver station.

An example of how the probability density distribution and the resultingselected subset of lower ordered MCS entries (S2) may reduce the bitrequirement for CQIs is described as follows with reference to FIG. 6B.In particular, FIG. 6B illustrates the ordered MCS entries table ofFIGS. 4 and 5 with the probability density distribution and the selectedset (S2) of FIG. 6A superimposed on top of the table. Suppose a firstCQI (CQI 1) associated with a highest quality channel of a set ofspatial channels (i.e., set of spatial channels linking a receiverstation to a transmitter station) requires 5 bits in order to directlyidentify one MCS entry out of the 32 MCS entries, in this case, MCS9. Inorder for the second CQI (CQI 2) to indirectly identify a second MCSentry, a selected subset of entries, S2, may be determined based atleast on the MCS probability density distribution. Members of S2, inthis case are entries MCS7, MCS6, MCS4, and MCS1. S2, as depicted, hasonly four entries instead of eight as was the case of conventionalsystems as described previously for FIG. 4.

As a result, only two bits (rather than the three bits needed forconventional systems) may be needed in order to at least indirectlyidentify the second MCS entry for CQI 2. That is, if the transmitterdevice (i.e., base station 210) receiving the CQI 2 (with the two bitsindirectly identifying the second MCS entry) is already provisioned withthe ordered MCS entries table (of FIGS. 4, 5, and 6B), and theprobability density distribution or the selected subset of FIG. 6A, itcan determine the identity of the second MCS, as indirectly identifiedby CQI 2, given the first MCS as directly identified by CQI 1.Similarly, for CQI 3, the select subset of non-continuous lower orderedMCS entries, if the selected subset is generic, may be used tofacilitate identification of a third MCS entry that is indirectlyidentified with a two bit CQI 3 given the second MCS entry that wasindirectly identified by CQI 2.

On the other hand, if the MCS probability density distribution and/orthe selected subset are not generic, than a new MCS probability densitydistribution and/or the selected subset may be determined for CQI 3,given CQI 2. The determination of the MCS probability densitydistribution may be performed, in some embodiments, while offline. Insuch a scenario, once the selected subset is determined based on the MCSprobability density distribution determined offline, the receiverstation may generate and provide a feedback (i.e., CQI indirectlyidentifying an MCS) according to the subset and the transmitter stationmay then select a MCS according to the subset and the feedback, whichmay occur during usage mode (i.e., when online).

It should be noted that it may be possible that for the second CQI, CQI2, the actual MCS entry should be an MCS entry other than those includedin the selected subset (i.e., MCS7, MCS6, MCS4, and MCS1). For example,suppose the actual MCS entry for CQI 2 should be MCS2, which is not amember of the selected subset. Such a discrepancy may be ignored sincethe MCS entry can be rounded to a selected subset member, such as MCS1.Further, the MCS entry (i.e., MCS1) to be indirectly identified by CQI 2using the rounding-off approach, which again may not be the actual MCSvalue, may be associated with a very low quality channel thus resultingin such a spatial channel not being used at all since such a spatialchannel may be undesirable for transmitting data signals. Thus, therounding-off approach, particularly when used for lower ordered MCSentries, may not impact the overall performance of a closed-loop MIMOsystem. Note that in some embodiments, one of the MCS entries of theselected subset may be reserved for no data transmission for thecorresponding spatial channel, i.e. spatial channel 2.

FIG. 7 depicts a process in accordance with various embodiments of thepresent invention. The example process 700 of FIG. 7 may be implementedas machine-accessible instructions utilizing any of many differentprogramming codes stored on any combination of machine-accessible mediasuch as a volatile or non-volatile memory or other mass storage device(e.g., a floppy disk, a CD, and a DVD). For example, themachine-accessible instructions may be embodied in a machine-accessiblemedium such as a programmable gate array, an application-specificintegrated circuit (ASIC), an erasable programmable read only memory(EPROM), a read only memory (ROM), a random access memory (RAM), amagnetic media, an optical media, and/or any other suitable type ofmedium. Further, although a particular order of actions is illustratedin FIG. 7, these actions may be performed in other temporal sequences.

In the example of FIG. 7, the process 700 may begin when an MCSprobability density function is determined for a second exemplaryspatial channel given a first exemplary spatial channel at 710. Such aprobability density function may be for provisioning a transmitterstation (i.e., base station 210) for use by the transmitter station inconjunction with CQIs received from a receiver station to select an MCSto transmit signals to the receiver station over the second spatialchannel.

A selected subset of lower ordered MCS entries relative to an MCS entryassociated with the first exemplary spatial channel may be determinedbased on the MCS probability density function at 720. In someembodiments, four lower ordered MCS entries may be included in thesubset. For these embodiments, the selected subset may be a selectedsubset of non-continuous lower ordered MCS entries wherein at least twosuccessively lower ordered MCS entries of the four lower ordered MCSentries are not immediately successive. An MCS entry from within thesubset may be selected for the second exemplary spatial channel at 730.

Although in some embodiments of the present inventions the methods andapparatuses described in this description may be associated with theThird Generation Partnership Project (3GPP) for the Long Term Evolution(LTE), the methods and apparatuses described in this description may bereadily applicable with other suitable wireless technologies, protocols,and/or standards.

FIG. 8 illustrates a block diagram of an apparatus in accordance withvarious embodiments of the present invention. For the embodiments, theapparatus 800 may be employed by or is part of, for example, a receiverstation to provide, among other things, one or more CQIs to atransmitter station. As shown, the apparatus 800 includes a controller810 and one or more monitors 820, coupled together as shown. Theapparatus 800 may further include a plurality of antennas 830 that maybe designed to communicate in a wireless network such as a WMAN. Notethat although three antennas 830 are depicted, in alternativeembodiments, fewer or more antennas may be employed. The components ofthe apparatus 800 may be used to perform the various methods andoperations described above. For example, the one or more monitors 820may be designed to measure channel quality associated with the apparatus800 receiving signals from a transmitter station for a first and asecond spatial channel. In some embodiments, the apparatus and thetransmitter station may employ a closed-loop MIMO system.

In contrast, the controller 810 may be designed to determine a first anda second CQI associated with the first and the second spatial channel,based at least in part on the channel qualities measured by the one ormore monitors 820, to directly and indirectly identify a first and asecond MCS entry among a plurality of ordered MCS entries, respectively.The second MCS entry to be determined by the controller 810 may be alower ordered MCS entry than the first MCS entry, the second MCS entrybeing one of a selected subset of non-continuous or continuous lowerordered MCS entries relative to the first MCS entry. The first and thesecond CQI that are determined by the controller 810 may be fortransmission to the transmitter station for use by the transmitterstation to transmit signals to the receiver station over the first andthe second spatial channel, respectively.

According to various embodiments of the present invention, thecontroller 810 may be further designed to generically or non-genericallypre-determine the selected subset of lower ordered MCS entries. For theembodiments, the pre-determined selected subset may be continuous ornon-continuous lower ordered MCS entries. The controller 810 maypre-determine the selected subset of lower ordered MCS entries bygenerating an MCS probability density distribution for a secondexemplary spatial channel, given a first exemplary spatial channel.After pre-determining the selected subset of non-continuous orcontinuous lower ordered MCS entries, the controller 810 may be adaptedto prompt the apparatus 800 to provide the pre-determined selectedsubset of non-continuous or continuous lower ordered MS entries to thetransmitter station.

The first CQI determined by the controller 810 may directly index thefirst MCS entry in the ordered MCS entries, and the second CQIdetermined by the controller 810 may indirectly index the second MCS inthe ordered MCS entries by indexing an MCS entry within the selectedsubset of non-continuous or continuous lower ordered MCS entriesrelative to the indexed first MCS entry. The controller 800 may befurther adapted to determine a third CQI, to indirectly identify a thirdMCS entry among the ordered MCS entries, the third MCS entry being alower ordered MCS entry than the second MCS entry. The above operationsmay be repeatedly performed by the apparatus 800 for additional CQIs(e.g., a fourth CQI, a fifth CQI, and so forth) if additional CQIs areto be provided to a transmitter station.

FIG. 9 is a block diagram of a system 2000 adapted to implement themethods and operations described previously. The system 2000 may be adesktop computer, a laptop computer, a handheld computer, a web tablet,a personal digital assistant (PDA), a server, a set-top box, a smartappliance, a pager, a text messenger, a game device, a wireless mobilephone and/or any other type of computing device.

The system 2000 illustrated in FIG. 9 includes a chipset 2010, whichincludes a memory controller 2012 and an input/output (I/O) controller2014. The chipset 2010 may provide memory and I/O management functionsas well as a plurality of general purpose and/or special purposeregisters, timers, etc. that are accessible or used by a processor 2020.In some embodiments, the chipset 2010 may be a communication chipsetconfigured to receive data signals from a transmitter station and toprovide to the transmitter station channel quality indicators (CQIs).The CQIs provided to the transmitter station may be correspondinglyassociated with the antennas for the transmitter station and may be usedby the transmitter station to select modulation coding schemes (MCSs)for use to transmit the data signals to the system. At least a first oneof the CQIs provided back to the transmitter station may directlyidentify a first MCS among a plurality of ordered MCS entries, and asecond one of the CQIs to indirectly identify a second MCS among theplurality of ordered MCS entries, the second MCS entry being one of aselected subset of non-continuous lower ordered MCS entries relative tothe first MCS entry.

The processor 2020 may be implemented using one or more processors, WLANcomponents, WMAN components, WWAN components, and/or other suitableprocessing components. For example, the processor 2020 may beimplemented using one or more of the Intel® Pentium® technology, theIntel® Itanium® technology, the Intel® Centrino™ technology, the Intel®Xeon™ technology, and/or the Intel® XScale® technology. In thealternative, other processing technology may be used to implement theprocessor 2020. The processor 2020 may include a cache 2022, which maybe implemented using a first-level unified cache (L1), a second-levelunified cache (L2), a third-level unified cache (L3), and/or any othersuitable structures to store data.

The memory controller 2012 may perform functions that enable theprocessor 2020 to access and communicate with a main memory 2030including a volatile memory 2032 and a non-volatile memory 2034 via abus 2040. The volatile memory 2032 may be implemented by SynchronousDynamic Random Access Memory (SDRAM), Dynamic Random Access Memory(DRAM), RAMBUS Dynamic Random Access Memory (RDRAM), and/or any othertype of random access memory device. The non-volatile memory 2034 may beimplemented using flash memory, Read Only Memory (ROM), ElectricallyErasable Programmable Read Only Memory (EEPROM), and/or any otherdesired type of memory device.

The processor system 2000 may also include an interface circuit 2050that is coupled to the bus 2040. The interface circuit 2050 may beimplemented using any type of interface standard such as an Ethernetinterface, a universal serial bus (USB), a third generation input/outputinterface (3GIO) interface, and/or any other suitable type of interface.

One or more input devices 2060 may be connected to the interface circuit2050. The input device(s) 2060 permit an individual to enter data andcommands into the processor 2020. For example, the input device(s) 2060may be implemented by a keyboard, a mouse, a touch-sensitive display, atrack pad, a track ball, an isopoint, and/or a voice recognition system.

One or more output devices 2070 may also be connected to the interfacecircuit 2050. For example, the output device(s) 2070 may be implementedby display devices (e.g., a light emitting display (LED), a liquidcrystal display (LCD), a cathode ray tube (CRT) display, a printerand/or speakers). The interface circuit 2050 may include, among otherthings, a graphics driver card.

The processor system 2000 may also include one or more mass storagedevices 2080 to store software and data. Examples of such mass storagedevice(s) 2080 include floppy disks and drives, hard disk drives,compact disks and drives, and digital versatile disks (DVD) and drives.

The interface circuit 2050 may also include a communication device suchas a modem or a network interface card to facilitate exchange of datawith external computers via a network. Although not depicted, coupled tothe interface circuit 2050 may be a plurality of antennas such as aplurality of omnidirectional antennas. In some embodiments, the antennasmay be designed to communicate in a wireless network such as a WMAN.

Access to the input device(s) 2060, the output device(s) 2070, the massstorage device(s) 2080 and/or the network may be controlled by the I/Ocontroller 2014. In particular, the I/O controller 2014 may performfunctions that enable the processor 2020 to communicate with the inputdevice(s) 2060, the output device(s) 2070, the mass storage device(s)2080 and/or the network via the bus 2040 and the interface circuit 2050.

While the components shown in FIG. 9 are depicted as separate blockswithin the processor system 2000, the functions performed by some ofthese blocks may be integrated within a single semiconductor circuit ormay be implemented using two or more separate integrated circuits. Forexample, although the memory controller 2012 and the I/O controller 2014are depicted as separate blocks within the chipset 2010, the memorycontroller 2012 and the I/O controller 2014 may be integrated within asingle semiconductor circuit.

Although certain embodiments have been illustrated and described herein,it will be appreciated by those of ordinary skill in the art that a widevariety of alternate and/or equivalent embodiments or implementationscalculated to achieve the same purposes may be substituted for theembodiments shown and described without departing from the scope of thepresent invention. Those with skill in the art will readily appreciatethat embodiments in accordance with the present invention may beimplemented in a very wide variety of ways. This application is intendedto cover any adaptations or variations of the embodiments discussedherein. Therefore, it is manifestly intended that embodiments inaccordance with the present invention be limited only by the claims andthe equivalents thereof.

1. A method comprising: measuring at a receiver station channelqualities associated with receiving signals from a transmitter stationfor a first and a second spatial channel, the transmitter and receiverstations employing a closed-loop multiple-input multiple-output (MIMO)system; and transmitting from the receiver station to the transmitterstation a first and a second channel quality indicator (CQI) to directlyand indirectly identify a first and a second modulation coding scheme(MCS) entry among a plurality of ordered MCS entries, respectively, thesecond MCS entry being one of a selected subset of lower ordered MCSentries relative to the first MCS entry, the first and second MCSentries correspondingly identifying a first and a second MCS for use bythe transmitter station to transmit signals to the receiver station overthe first and the second spatial channel, and the CQIs having beendetermined based at least in part on the measured channel qualities. 2.The method of claim 1, wherein the first CQI directly indexes the firstMCS entry in the ordered MCS entries, and the second CQI indirectlyindexes the second MCS in the ordered MCS entries by indexing an MCSentry within the selected subset of lower ordered MCS entries relativeto the indexed first MCS entry.
 3. The method of claim 2, wherein theselected subset of lower ordered MCS entries are a selected subset ofcontinuous lower ordered MCS entries.
 4. The method of claim 2, whereinthe selected subset is a selected subset of non-continuous lower orderedMCS entries having at least two successively lower ordered MCS entriesthat are not immediately successive.
 5. The method of claim 2 furthercomprising pre-determining by the receiver station the selected subsetof lower ordered MCS entries.
 6. The method of claim 5, furthercomprising the receiver station providing the pre-determined selectedsubset of lower ordered MCS entries to the transmitter station.
 7. Themethod of claim 5, wherein the pre-determining comprises generating anMCS probability density distribution for a second exemplary spatialchannel given a first exemplary spatial channel.
 8. The method of claim1, further comprising transmitting from the receiver station to thetransmitter station a third CQI to indirectly identify a third MCS entryamong the ordered MCS entries, the third MCS entry being a lower orderedMCS than the second MCS entry.
 9. The method of claim 1, wherein thefirst CQI and the second CQI are associated with the first and thesecond spatial channel, respectively, and the method further comprisingtransmitting from the receiver station to the transmitter station afirst and a second beamforming vector for the first and the secondspatial channels, respectively, the first and the second beamformingvectors transmitted in order to indicate to the transmitter stationorder of the first and the second CQI.
 10. The method of claim 9,wherein the first and the second beamforming vectors are transmitted tothe transmitter station to indicate to the transmitter station that thefirst CQI is associated with the first spatial channel that is a higherquality channel than the second spatial channel associated with thesecond CQI.
 11. An apparatus comprising: one or more monitors to measurechannel qualities associated with the apparatus receiving signals from atransmitter station for a first and a second spatial channel, theapparatus and the transmitter station employing a closed-loopmultiple-input multiple-output (MIMO) system; and a controller coupledto the one or more monitors to determine a first and a second channelquality indicator (CQI) to directly and indirectly identify a first anda second modulation coding scheme (MCS) entry among a plurality ofordered MCS entries, respectively, the second MCS entry being a lowerordered MCS entry of the two, the second MCS entry being one of aselected subset of lower ordered MCS entries relative to the first MCSentry, the first and the second CQI for transmission to the transmitterstation for use by the transmitter station to identify a first and asecond MCS correspondingly identified by the first and second MCSentries for use to transmit signals to the receiver station over thefirst and the second spatial channel, and the CQIs having beendetermined based at least in part on the channel qualities measured bythe one or more monitors.
 12. The apparatus of claim 11, wherein thecontroller is adapted to determine the first CQI that directly indexesthe first MCS entry in the ordered MCS entries, and to determine thesecond CQI that indirectly indexes the second MCS in the ordered MCSentries by indexing an MCS entry within the selected subset of lowerordered MCS entries relative to the indexed first MCS entry.
 13. Theapparatus of claim 12, wherein the controller is further adapted topre-determine the selected subset of lower ordered MCS entries.
 14. Theapparatus of claim 13, wherein the controller is further adapted toprompt the apparatus to provide the pre-determined selected subset oflower ordered MCS entries to the transmitter station.
 15. The apparatusof claim 13, wherein the controller is further adapted to saidpre-determine the selected subset of lower ordered MCS entries bygenerating an MCS probability density distribution for a second spatialchannel given a first spatial channel.
 16. The apparatus of claim 11,wherein the controller is adapted to determine a third CQI to indirectlyidentify a third MCS entry among the ordered MCS entries, the third MCSentry being a lower ordered MCS than the second MCS entry.
 17. Anarticle of manufacture comprising: a storage medium; and a plurality ofprogramming instructions configured to program an apparatus to enablethe apparatus to determine a modulation coding scheme (MCS) probabilitydensity function for a second exemplary spatial channel given a firstexemplary spatial channel for provision to a transmitter station, foruse by the transmitter station in conjunction with channel qualityindicators (CQIs) received from a receiver station to select an MCS totransmit signals to the receiver station over a spatial channel.
 18. Thearticle of claim 17, wherein said instructions are adapted to enablesaid apparatus to determine, based on the MCS probability densityfunction, a selected subset of lower ordered MCS entries relative to anMCS entry associated with the first exemplary spatial channel, saidselection of the MCS to be from within the subset.
 19. The article ofclaim 18, wherein said instructions are adapted to enable said apparatusto determine said selected subset of lower ordered MCS entries bydetermining a selected subset of continuous lower ordered MCS entries.20. The article of claim 18, wherein said instructions are adapted toenable said apparatus to said determine four lower ordered MCS entriesby determining a selected subset of non-continuous lower ordered MCSentries having at least two successively lower ordered MCS entries ofthe four lower ordered MCS entries that are not immediately successive.21. A system comprising: a plurality of omnidirectional antennas; aprocessor; and a communication chipset coupled to the antennas and theprocessor, and configured to receive data signals from a transmitterstation and to provide to the transmitter station channel qualityindicators (CQIs) correspondingly associated with the antennas for thetransmitter station to select modulation coding schemes (MCSs) for useto transmit the data signals to the system, a first one of the CQIs todirectly identify a first MCS entry among a plurality of ordered MCSentries, and a second one of the CQIs to indirectly identify a secondMCS entry among the plurality of ordered MCS entries, the second MCSentry being one of a selected subset of lower ordered MCS entriesrelative to the first MCS entry, and the first and second MCS entriescorrespondingly identify a first and a second MCS.
 22. The system ofclaim 21, wherein the plurality of antennas are designed to communicatein a wireless metropolitan area network (WMAN).
 23. The system of claim21, wherein the system is one selected from the group consisting of adesktop computer, a laptop computer, a set-top box, a personal digitalassistant (PDA), a web tablet, a pager, a text messenger, a game device,a smart appliance, or a wireless mobile phone.